The present invention relates to a method for computing a charging capacity of a battery, which supplies the electric power to loads in a vehicle, and an apparatus for use in such method. More specifically, the present invention relates to a method and an apparatus for computing a charging capacity of a battery, in which a voltage-current characteristic derived from a periodically measured terminal voltage and discharge current of the battery is used to estimate an estimated voltage that is an estimated terminal voltage of the battery in its state of constant-load discharge, thereby the charging capacity of the battery is computed from the estimated voltage.
So far, a driving source of a vehicle has been mainly an engine, in which gasoline or gas oil is employed as the fuel, but in recent years a vehicle employing an electromotive motor, which does not directly discharge the combustion gas, as the only or the supplementary driving source has appeared. As to a vehicle loading the electromotive motor, grasping a charging capacity of a battery, which supplies the electric power to the electromotive motor, is important for computing a possible traveling distance and so on.
So far, an integration method of current or electric power has been employed, in which an integrated consumed electric power computed by using an integrated value of the discharge current is subtracted from a full charging capacity so as to compute the present charging capacity. However, in such a method, an original full charging capacity is changed depending upon individual differences among batteries, deterioration rates of the batteries and so on, therefore the present charging capacity of the battery cannot be accurately computed.
A state of charge of the battery can be known by measuring the density of the electrolyte of the battery since there is a certain linear relationship between the density of the electrolyte and the state of charge. However, actually in a battery during charging or discharging and a battery right after the completion of charge or discharge thereof, chemical reactions occurring between the electrolyte and the electrodes make the density of the electrolyte non-uniform, therefore the state of charge of the battery cannot be known accurately by measuring the density of the electrolyte.
Besides, the charging capacity of the battery may be known by measuring the terminal voltage of the battery. But the terminal voltage is not stable unless the discharge current is stabilized, therefore actually the terminal voltage correlating with the state of charge of the battery cannot be obtained by the measurement.
As shown in characteristic graphs in FIG. 11, in which the battery is subjected to the discharge with each constant current ranging from 10 to 80 A in units of 10 A, the discharging time (horizontal axis) increases with decreasing the discharge current while the terminal voltage (vertical axis) of the battery drastically decreases with the discharging time.
Here, the horizontal axis of the characteristic graphs in FIG. 11 is the time, however, since the discharge is carried out with the constant current and the battery capacity is expressed by electrical quantity (Ah), this horizontal axis can be regarded as the battery capacity.
Then, the characteristic graphs in FIG. 11 reveals that smaller the discharge current, higher the electric power to be obtained and that the capacity drop near the state of full charge of the battery is slow while the capacity drop near the state of full discharge is rapid.
As described above, even if the discharge current can be stabilized, since there is no linear correlation between the charging capacity of the battery and the terminal voltage thereof, the charging capacity cannot be derived from the terminal voltage of the battery.
Thus, appears to be reasonable is a method for computing the capacity employing a relationship between the state of charge of the battery and the open circuit voltage, which is possibly a linear relationship since there is about a linear relation between the electrolyte density of the battery and the open circuit voltage and since there is a linear relation between the electrolyte density of the battery and the state of charge of the battery.
However, the sole weak point of this method for computing the capacity is that the open circuit voltage can be measured during non-discharging period of time when the state of charge of the battery does not change, except the self-discharging. In other words, the open circuit voltage cannot be measured during discharging when the state of charge of the battery changes.
Consequently, a point of the above method for computing the capacity is how to find out the open circuit voltage during the discharge of the battery.
The terminal voltage and the discharge current can be measured during the discharge of the battery. As shown in FIG. 11, since the terminal voltage appears to decrease with increasing the discharge current even when the state of charge of the battery does not change, there is a voltage-current characteristic (I-V characteristic) showing a negative correlation between the terminal voltage and the discharge current, which changes with changing the state of charge of the battery.
Thus, in order to know a plurality of the voltage-current characteristics of the battery in response to the state of charge of the battery, the following measurement is carried out.
First, a discharge is continuously carried out by using an impulse current, in which a current Ia and a current Ib smaller than Ia are periodically mutually appear, and then the predetermined number of the sets (for example, 100 sets) of the terminal voltage having a reverse phase with respect to the discharge current and the discharge current, i.e. (Ia, VI), (Ib, V2), (Ia, V3), (Ib, V4),xe2x80x94are continuously sampled at the same period of time with the impulse cycle (for example, 1 millisecond) of the discharge current.
Then, from thus sampled sets of the terminal voltage and the discharge current, i.e. (Ia, V01), (Ib, V02), (Ia, V03), (Ib, V04),xe2x80x94, by using the method of least squares, coefficients a1 and b1 in an equation V=all +b1, i.e. a linear relationship between the voltage and current of the battery are obtained, wherein the equation V=a1I+b1 is placed as the voltage-current characteristic of the battery corresponding to the capacity during the above sampling.
Then, the similar discharge to the discharge described above is continuously carried out by using an impulse current, in which currents Ia and Ia are periodically mutually appear, and then the predetermined number of the sets of the terminal voltage having a reverse phase with respect to the discharge current and the discharge current, i.e. (Ia, V11), (Ib, V12), (Ia, V13), (Ib, V14),xe2x80x94are continuously sampled. Then, from thus sampled sets of the terminal voltage and the discharge current, by using the method of least squares, coefficients a2 and b2 in an equation V=a2I +b2, i.e. a linear relationship between the voltage and current of the battery are obtained, wherein the equation V=a2I+b2 is placed as the voltage-current characteristic of the battery corresponding to the capacity during the above sampling.
Thereafter, similarly, coefficients an and bn in an equation V=a2I +b2, i.e. a linear relationship between the voltage and current of the battery are obtained, wherein the equation V=a2I+b2 is placed as the voltage-current characteristic of the battery corresponding to each mutually different capacity which gradually decreases, thereby the voltage-current characteristics of the battery corresponding to the respective capacities ranging from 100% to 0%.
In FIG. 12, there is schematically shown a relation between the sampled sets of the terminal voltage and the discharge current. i.e. (Ia Vn1), (Ib, Va2), (Ia, Vn3), (Ib, Vn4),xe2x80x94and the linear voltage-current equation V=anI +bn, which is obtained from the sets by using the method of least squares.
Here, an imaginary current value Is that is an imaginary constant current value is substituted to the voltage-current characteristic equation of the battery corresponding to the respective capacities, then if the resultant obtained V is defined as an estimated voltage Vn that is an estimated terminal voltage of the battery in its state of constant-load discharge, a constant current discharging characteristic shown in graphs in FIG. 13 is obtained.
When any positive value is substituted for the imaginary current value Is, the corresponding constant current discharging characteristic becomes a non-linear characteristic, in which the estimated terminal voltage Vn rapidly decreases as the capacity of the horizontal axis increases in the vicinity of the right end of the respective curves, and even in the case of the imaginary current value Is=0 A, in which the open circuit voltage must be theoretically shown, the constant current discharging characteristic shows a similar characteristic.
According to the graphs in FIG. 13, since smaller the imaginary current value Is, smaller the degree of decreasing in the estimated voltage Vn as the capacity reduces to zero, therefore when a negative value is substituted as the imaginary current value Is to the voltage-current characteristic equation of the battery corresponding to the respective capacities, the resultant constant current discharging characteristic is expressed by curves shown in FIG. 14. In this case, the characteristic of the estimated voltage Vn in the vicinity of the capacity being zero shows an inflectional change having a boundary of the imaginary current value Is=xe2x88x9210 A.
Consequently, theoretically if the imaginary current value Is is set xe2x88x9210 A, the estimated voltage Vn in the constant current discharge shows a linear relationship with respect to the capacity of the battery.
FIG. 15 shows graphs illustrating the voltage-current characteristic of the battery corresponding to the respective capacities with having the vertical axis of the discharge current I and the horizontal axis of the terminal voltage V. In the following, that the estimated voltage Vn during the constant current discharging has a linear relationship with respect to the battery capacity will be verified.
Since coefficients a1, a2,xe2x80x94, an, expressing the respective gradients of the voltage-current characteristic equations are mutually different and coefficients b1, b2xe2x80x94, bn expressing the respective intercepts of the voltage-current characteristic equations also are mutually different, in the region of positive discharge current that actually exists, no value I of discharge current, at which the terminal voltage V linearly changes with the change in the battery capacity, exists.
To the contrary, in the region of negative discharge current that is an imaginary region shown in FIG. 15, the terminal voltage V shows a characteristic of changing linearly with respect to the battery capacity, that is, the terminal voltage V of the battery corresponding to each capacity at the discharge current value I=xe2x88x9210 A is the estimated voltage Vn.
A graph in FIG. 16 shows a relationship between the battery capacity at the imaginary current value Is=xe2x88x9210 A and the estimated voltage Vn that has a linear correlation with the battery capacity. As shown in FIG. 16, the estimated voltage Vn exists between the open circuit voltage Vs at the fully charged state and the open circuit voltage Ve at the end of discharge, therefore a capacity value corresponding to the estimated voltage Vn is a residual capacity, i.e. a state of charge (SOC).
Consequently, since the estimated voltage takes the place of the open circuit voltage of the battery, even upon discharge when the open circuit voltage cannot be measured, provided that the discharge is a constant load discharge, in which the load supplying the electric power does not change during discharge, the terminal voltage that changes delicately during discharge and the discharge current are measured, thereby the voltage-current characteristic that is a relation between the terminal voltage and the discharge current during the constant load discharge is known. Then, the imaginary current value Is=xe2x88x9210 A is substituted into the resultant characteristic equation (V=aI+b) so as to know the estimated voltage Vn, thereby the a state of charge (SOC) of the battery can be calculated from the estimated voltage Vn.
The present state of charge (SOC) with respect to the fully charged capacity can be calculated from the graph shown in FIG. 16 as follows:
SOC={(Vnxe2x88x92Ve)/(Vsxe2x80x94Ve)}xc3x97100(%).
More accurately, the present state of charge (SOC) with respect to the fully charged capacity can be calculated as follows in terms of a ratio of the electric power (Vxc3x97Ah):                     SOC        =                  xe2x80x83                ⁢                  {                                    [                                                (                                      Vn                    +                    Ve                                    )                                /                2                            ]                        xc3x97                          [                                                (                                      Vn                    -                    Ve                                    )                                /                                  (                                      Vs                    -                    Ve                                    )                                            ]                        xc3x97            A            ⁢                          xe2x80x83                        ⁢            h            }            /                                                                        xe2x80x83                    ⁢                                                                      {                                                                                    [                                                  Vs                          +                          Ve                                                                    )                                        /                    2                                                  ]                            xc3x97              A              ⁢                              xe2x80x83                            ⁢              h                        }                          xc3x97        100        ⁢                  xe2x80x83                ⁢                  (          %          )                                                              =                          xe2x80x83                        ⁢                                          {                                                                            (                                                                        Vn                          2                                                -                                                  Ve                          2                                                                    )                                        /                                          Vs                      2                                                        -                                      Ve                    2                                                              )                                }                xc3x97        100        ⁢                  xe2x80x83                ⁢                              (            %            )                    .                    
Generally, as shown in FIG. 17, during the discharge of a battery, a voltage drop due to a pure resistance (ohmic resistance of the battery) such as IR drop (=the pure resistancexc3x97discharge current) and a voltage drop due to a polarization at the discharging side takes place, on the other hand during the charge of the battery, a voltage rise due to the pure resistance such as voltage rise due to a polarization at the charging side takes place.
Especially as shown in FIG. 17, an activation polarization for advancing redox reactions on the surface of the electrodes, which is included in the polarization at the discharging side arising during the discharge of the battery, and a concentration polarization due to the difference in concentrations of the reactants and products generated from a result of the mass transfer between the electrode surfaces and the solution, take place with some delay with respect to the increase and decrease in the discharge current, therefore these polarizations do not show a linear relationship with the value of the discharge current.
Consequently, when the estimated voltage Vn is to be caluculated instead of the open circuit voltage in order to compute the state of charge (SOC) of the battery, the terminal voltage and the discharge current are measured during the discharge so as to caluculate the voltage-current characteristic. However, since the terminal voltage includes the voltage drop due to the polarization during the discharge, the caluculated voltage-current characteristic and the estimated voltage Vn caluculated therefrom include the voltage drop due to the polarization besides the state of charge (SOC) of the battery, therefore the estimated voltage Vn as it is cannot employed to calculate accurately the state of charge (SOC) of the battery.
It is therefore an objective of the present invention to solve the above problem and to provide a method for computing a battery capacity, in which an estimated voltage, which is an estimated terminal voltage of the battery in its state of constant-load discharge and is calculated from a correlation between the terminal voltage and the discharge current that are measurable during the discharge, is employed to compute the state of charge of the battery, thereby the the state of charge of the battery can be accurately computed even if the terminal voltage of the battery, which is used to calculate the estimated voltage, does not completely cancel out the factors of voltage rise or drop due to the former charge or discharge. The present invention also provides an apparatus for use in such method.
A first aspect of the present invention is a method for computing a battery capacity comprising the steps of:
periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle;
calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic; and
computing a charging capacity of the battery from the estimated voltage,
wherein a value of the estimated voltage of the battery in the constant load discharge with a predetermined large current value is estimated from the voltage-current characteristic when the discharge current of the constant load discharging process by the battery that is in an equilibrium state is decreasing from the predetermined large current value corresponding to a maximum supplying electric power value to the loads,
a difference value between the value of the estimated voltage and a value of an open circuit voltage, which estimates the value of the estimated voltage and is a terminal voltage of the battery that is in an equilibrium state before the start of the constant load discharge by using the predetermined large current value, is calculated in advance as a value of a residual voltage drop due to a residual polarization at the end of the discharge process of the battery,
thereafter, whenever the battery is subjected to the constant load discharge by using the predetermined large current value, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured during the constant load discharge by using the predetermined large current value,
a present estimated voltage of the battery is estimated from the voltage-current characteristic, and
the value of the residual voltage drop is added to a value of the present estimated voltage of the battery, thereby a present charging capacity of the battery is computed.
According to the method for computing a battery capacity of the first aspect of the present invention, once the discharge current of the constant load discharge reaches the predetermined large current value corresponding to the maximum supply electric power value to the loads of the vehicle, even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, the system is in a state that the polarization of the discharge side corresponding to the predetermined large current value, which exceeds the residual voltage drop, arises or in a state that the polarization of the discharge side, the magnitude of which corresponds to the predetermined large current value, newly arises after the residual voltage rise is canceled off.
On the other hand, even if the battery in an equilibrium state is subjected to the constant load discharge with the predetermined large current value, when the discharge current reaches the predetermined large current value, the polarization arises, the magnitude of which corresponds to the predetermined large current value.
Therefore, when the battery is subjected to the constant load discharge with the predetermined large current value, not depending upon that the battery was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled off, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery while the discharge current is decreasing from the predetermined large current value, is the same.
Not depending upon whether or not the battery was in an equilibrium state before the start of the constant load discharge with the predetermined large current value, the value of the estimated voltage estimated after the start of the constant load discharge is lower than the open circuit voltage, corresponding to the terminal voltage of the battery in the equilibrium state when supposing that the battery before the start of the constant load discharge was in the equilibrium state, by the residual voltage drop value, which is in advance calculated as the value of the residual voltage drop due to the residual polarization at the end of the constant load discharge carried out by the battery with the predetermined large current value.
Preferably, regarding the method according to the first aspect of the present invention, a value of the terminal voltage of the battery in an equilibrium state is measured in advance so as to set up the measured value as a value of the open circuit voltage,
then, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process is decreasing from the predetermined large current value when the buttery in an equilibrium state is subjected to the constant load discharge by using the predetermined large current value,
then, the estimated voltage of the battery upon the constant load discharge by using the predetermined large current value starting from the equilibrium state is estimated from the voltage-current characteristic, and
then, a value of the estimated voltage of the battery upon the constant load discharge by using the predetermined large current value starting from the equilibrium state is subtracted from the value of the set open circuit voltage, thereby the value of the residual voltage drop is calculated in advance.
According to the method for computing a battery capacity of the first aspect of the present invention, when the battery in the equilibrium state implements the constant load discharge with the predetermined large current value, the terminal voltage of the battery is measured before the start of the constant load discharge so as to set up the value of the open circuit voltage, then when the discharge current of the constant load discharge decreases from the predetermined large current value, the estimated voltage is estimated on the basis of the voltage-current characteristic calculated from the periodically measured terminal voltage and discharge current of the battery, thereby the difference between the estimated voltage and the value of the open circuit voltage set up beforehand is calculated as the value of the residual voltage drop, thereafter the difference is added to the present estimated voltage of the battery, which is estimated each time the battery is subjected to the constant load discharge, this addition being implemented in order to compute the present charging capacity of the battery.
Preferably, regarding the method according to the first aspect of the present invention, whenever the battery reaches an equilibrium state, the value of the open circuit voltage is newly replaced by a value of the terminal voltage of the battery, which is measured in the equilibrium state.
According to the method for computing a battery capacity of the first aspect of the present invention, the open circuit voltage changing in response to the change in the state of charge due to the discharge is replaced by the newest value of the terminal voltage each time the battery is in an equilibrium state.
Preferably, regarding the method according to the first aspect of the present invention, whenever the battery is subjected to the constant load discharge by using the predetermined large current value, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process by using the predetermined large current value is decreasing from the predetermined large current value, thereby the present estimated voltage of the battery is estimated from the voltage-current characteristic.
According to the method for computing a battery capacity of the first aspect of the present invention, whenever the battery is subjected to the constant load discharge by using the predetermined large current value, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process by using the predetermined large current value is decreasing from the predetermined large current value, thereby the present estimated voltage of the battery is estimated from the voltage-current characteristic and the present state of charge of the battery is computed from the values of the estimated voltage and the residual voltage drop.
Preferably, regarding the method according to the first aspect of the present invention, the predetermined large current value is set to be a current value required upon starting a starter motor of the vehicle, and the voltage-current characteristic is calculated from the terminal voltage and the discharge current, which are periodically measured while the value of the discharge current decreases to a target current value that is smaller than the predetermined large current value and not less than a maximum discharge current value when loads of the vehicle except the starter motor are driven, after the value of the discharge current starts to decrease from the predetermined large current value.
According to the method for computing a battery capacity of the first aspect of the present invention, even if the electric power from the battery is simultaneously supplied to a plurality of the other loads of the vehicle, the current value required upon the start of the starter motor exceeds the current value thereof, therefore when the current value required upon the start of the starter motor is set up to be the predetermined large current value, the terminal voltage is subjected to the voltage drop exceeding the voltage drop due to the polarization of the discharge side arisen due to the former discharge when the discharge current reaches the predetermined large current.
On the other hand, when the discharge current decreases from the predetermined large current value to the target current value not less than the maximum discharge current value upon the driving of the loads except the starter motor, the voltage drop due to the polarization of the discharge side remaining in the terminal voltage of the battery in that state does not seemingly contain the voltage drop component due to the polarization of the discharge side arisen due to the power supply to the loads of the vehicle except the starter motor, therefore only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, seemingly appears.
Consequently, when the voltage-current characteristic is calculated from the terminal voltage and discharge current periodically measured until the discharge current of the battery, which carries out the constant load discharge with the predetermined large current value, decreases from the predetermined large current value to the target current value, the estimated voltage estimated from the the voltage-current characteristic purely reflects only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, even if the loads of the vehicle except the starter motor is still driven.
Preferably, regarding the method according to the first aspect of the present invention, whenever the estimated voltage of the battery is estimated upon the constant load discharge by using the predetermined large current value, the value of the residual voltage drop is revised in response to a circumferential temperature of the battery upon the estimation of the estimated voltage and a circumferential temperature of the battery upon the calculation of the open circuit voltage, and the present charging capacity of the battery is computed from the revised value of the residual voltage drop.
According to the method for computing a battery capacity of the first aspect of the present invention, when the temperature around the battery changes, the battery capacity also changes to change the terminal voltage of the battery, therefore if the temperature around the battery is different between at a time when the open circuit voltage of the battery in an equilibrium is calculated and at a time when the estimated voltage of the battery is estimated during the constant load discharge by using the predetermined large current value, the terminal voltage component reflected in the open circuit voltage in response to the temperature around the battery is different from the terminal voltage component reflected in the estimated voltage in response to the temperature around the battery.
However, if the present charging capacity of the battery is computed by using the revised value of the residual voltage drop, which is revised in response to the temperature around the battery when the open circuit voltage of the battery in an equilibrium is calculated and the temperature around the battery when the estimated voltage of the battery is estimated during the constant load discharge by using the predetermined large current value, the present state of charge of the battery is computed in a state that the changeable component of the terminal voltage changeable due to the difference in the temperature around the battery is removed, by using the open circuit voltage and estimated voltage, in which the terminal voltage component in response to the temperature around the battery is reflected in the same condition.
A second aspect of the present invention is a method for computing a battery capacity comprising the steps of:
periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle;
calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic; and
computing a charging capacity of the battery from the estimated voltage,
wherein whenever the battery is subjected to the constant load discharge by using the predetermined large current value corresponding to a maximum supplying electric power value to the loads, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process by using the predetermined large current value is decreasing from the predetermined large current value, thereby the present estimated voltage Vn of the battery is estimated from the voltage-current characteristic.
According to the method for computing a battery capacity of the second aspect of the present invention, once the discharge current of the constant load discharge reaches the predetermined large current value corresponding to the maximum supplying electric power value to the loads of the vehicle, even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, the system is in a state that the polarization of the discharge side corresponding to the predetermined large current value, which exceeds the residual voltage drop, arises or in a state that the polarization of the discharge side, the magnitude of which corresponds to the predetermined large current value, newly arises after the residual voltage rise is canceled off.
On the other hand, even if the battery in an equilibrium state is subjected to the constant load discharge with the predetermined large current value, when the discharge current reaches the predetermined large current value, the polarization arises, the magnitude of which corresponds to the predetermined large current value.
Therefore, when the battery is subjected to the constant load discharge with the predetermined large current value, not depending upon that the battery was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled off, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery while the discharge current is decreasing from the predetermined large current value, is the same.
When the battery implements the constant load discharge with the predetermined large current, even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured until the discharge current value decreases from the predetermined large current value under the condition that the influence of the residual voltage drop or rise is removed, then this voltage-current characteristic, in which the influence of the polarization arisen in the former discharge is removed, is used to estimate the present estimated voltage of the battery, thereby the state of charge of the battery is computed.
Preferably, regarding the method according to the second aspect of the present invention, the predetermined large current value is set to be a current value required upon starting a starter motor of the vehicle.
According to the method for computing a battery capacity of the second aspect of the present invention, even if the electric power from the battery is simultaneously supplied to a plurality of the other loads of the vehicle, the current value required upon the start of the starter motor exceeds the current value thereof, therefore when the current value required upon the start of the starter motor is set up to be the predetermined large current value, the terminal voltage is subjected to the voltage drop exceeding the voltage drop due to the polarization of the discharge side arisen due to the former discharge when the discharge current reaches the predetermined large current.
Preferably, regarding the method according to the second aspect of the present invention, the voltage-current characteristic is calculated from the terminal voltage and the discharge current, which are periodically measured while the value of the discharge current decreases to a target current value that is smaller than the predetermined large current value and not less than a maximum discharge current value when loads of the vehicle except the starter motor are driven.
According to the method for computing a battery capacity of the second aspect of the present invention, when the discharge current decreases from the predetermined large current value to the target current value not less than the maximum discharge current value upon the driving of the loads except the starter motor, the voltage drop due to the polarization of the discharge side remaining in the terminal voltage of the battery in that state does not seemingly contain the voltage drop component due to the polarization of the discharge side arisen due to the power supply to the loads of the vehicle except the starter motor, therefore only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, seemingly appears.
Consequently, when the voltage-current characteristic is calculated from the terminal voltage and discharge current periodically measured until the discharge current of the battery, which carries out the constant load discharge with the predetermined large current value, decreases from the predetermined large current value to the target current value, the estimated voltage estimated from the the voltage-current characteristic purely reflects only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, even if the loads of the vehicle except the starter motor is still driven.
As shown in FIG. 1, the first aspect of the present invention is also an apparatus for computing a battery capacity executing the steps of:
periodically measuring a terminal voltage and a discharge current of a battery 13 that supplies an electric power to loads in a vehicle when the battery 13 is subjected to a constant load discharge by using a predetermined large current value corresponding to a maximum supplying electric power value to the loads;
calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
estimating an estimated voltage that is an estimated terminal voltage of the battery 13 in a constant load discharging state thereof from the voltage-current characteristic; and
computing a charging capacity of the battery 13 from the estimated voltage,
wherein the apparatus comprises first memory means 27 for memorizing a difference value as a value of a residual voltage drop due to a residual polarization at the end of the discharge process of the battery 13, said difference value being a difference value between a value of the estimated voltage and a value of an open circuit voltage,
in which the value of the estimated voltage of the battery 13 in the constant load discharge with a predetermined large current value is estimated from the voltage-current characteristic when the discharge current of the constant load discharging process by the battery 13 that is in an equilibrium state is decreasing from the predetermined large current value, and
the open circuit voltage estimates the value of the estimated voltage and is a terminal voltage of the battery 13 that is in an equilibrium state before the start of the constant load discharge by using the predetermined large current value,
and wherein the value of the residual voltage drop memorized by the first memory means 27 is added to the value of the estimated voltage of the battery 13, thereby a present charging capacity of the battery 13 is computed.
According to the apparatus for computing a battery capacity of the first aspect of the present invention, once the discharge current of the constant load discharge reaches the predetermined large current value corresponding to the maximum supply electric power value to the loads of the vehicle, even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, the system is in a state that the polarization of the discharge side corresponding to the predetermined large current value, which exceeds the residual voltage drop, arises or in a state that the polarization of the discharge side, the magnitude of which corresponds to the predetermined large current value, newly arises after the residual voltage rise is canceled off.
On the other hand, even if the battery 13 in an equilibrium state is subjected to the constant load discharge with the predetermined large current value, when the discharge current reaches the predetermined large current value, the polarization arises, the magnitude of which corresponds to the predetermined large current value.
Therefore, when the battery 13 is subjected to the constant load discharge with the predetermined large current value, not depending upon that the battery 13 was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled off, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery 13 while the discharge current is decreasing from the predetermined large current value, is the same.
Not depending upon whether or not the battery 13 was in an equilibrium state before the start of the constant load discharge with the predetermined large current value, the value of the estimated voltage estimated after the start of the constant load discharge is lower than the open circuit voltage, corresponding to the terminal voltage of the battery 13 in the equilibrium state when supposing that the battery 13 before the start of the constant load discharge was in the equilibrium state, by the residual voltage drop value, which is in advance calculated as the value of the residual voltage drop due to the residual polarization at the end of the constant load discharge carried out by the battery 13 with the predetermined large current value.
Preferably, regarding the apparatus according to the first aspect of the present invention, the apparatus further comprises:
first detecting means A for detecting a start of a decrease in the discharge current from the predetermined large current value in the constant load discharge process of the battery 13 by using the predetermined large current value;
first calculating means 23A for calculating the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery 13 after the first detecting means A detects the start of the decrease in the discharge current; and
estimating means 23B for estimating the estimated voltage of the battery 13 in the constant load discharge process of the battery 13 by using the predetermined large current value, on the basis of the voltage-current characteristic calculated by the first calculating means 23A, wherein the value of the residual voltage drop memorized by the first memory means 27 is added to a value of the estimated voltage of the battery 13 estimated by the estimating means 23B, thereby a present charging capacity of the battery is computed.
According to the apparatus for computing a battery capacity of the first aspect of the present invention, when the battery 13 implements the constant load discharge with the predetermined large current value, each time the first detecting means A detects a start of a decrease in the discharge current of the battery 13 from the predetermined large current value, the first calculating means 23A calculates the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery 13, which are periodically measured while the discharge current decreases from the predetermined large current value, then the estimating means estimates the estimated voltage of the battery 13 in the constant load discharge process of the battery by using the predetermined large current value, on the basis of the voltage-current characteristic calculated by the first calculating means 23A, the present state of charge of the battery 13 is computed from the value of the residual voltage drop memorized by the first memory means 27 and the value of the estimated voltage estimated by the estimating means 23B.
Preferably, regarding the apparatus according to the first aspect of the present invention, the apparatus further comprises:
second memory means 25 for memorizing the value of the open circuit voltage;
judging means 23C for judging whether the battery is in an equilibrium state or not; and
second calculating means 23D for calculating the value of the residual voltage drop by subtracting the estimated voltage estimated by the estimating means 23B from the value of the open circuit voltage memorized by the second memory means 25 in the constant load discharge process of the battery, which is judged to be in an equilibrium state by the judging means 23C, by using the predetermined large current value,
wherein the first memory means 27 memorizes the value of the residual voltage drop calculated by the second calculating means 23D.
According to the apparatus for computing a battery capacity of the first aspect of the present invention, when the battery 13, which is judged to be in an equilibrium state by the judging means 23C, implements the constant load discharge with the predetermined large current value, after the first detecting means A detects that the charge current of the battery 13 decreases from the predetermined large current value, the second calculating means 23D calculates the value of the residual voltage drop by subtracting the estimated voltage estimated by the estimating means 23B from the value of the open circuit voltage memorized by the second memory means 25, then the first memory means 27 memorizes the value of the residual voltage drop calculated by the second calculating means 23D.
Preferably, regarding the apparatus according to the first aspect of the present invention, the apparatus further comprises:
measuring means B for measuring the terminal voltage of the battery 13, which is judged to be in an equilibrium state by the judging means 23C; and
replacing means 23E for replacing the value of the open circuit voltage memorized by the second memory means 25 with a value of the terminal voltage of the battery 13 measured by the measuring means B.
According to the apparatus for computing a battery capacity of the first aspect of the present invention, even if the open circuit voltage of the battery 13 changes in response to the change in the state of charge due to the discharge, each time the battery 13 is judged to be in an equilibrium state by the judging means 23C, the value of the open circuit voltage memorized by the second memory means 25 is replaced with the newest value of the terminal voltage of the battery 13 measured by the measuring means B.
Preferably, regarding the apparatus according to the first aspect of the present invention, the apparatus further comprises:
second detecting means 19 for detecting a circumferential temperature of the battery 13; and
revising means 23F for revising the value of the residual voltage drop memorized by the first memory means 27 in response to the circumferential temperature of the battery 13 detected by the second detecting means 19 when the estimating means 23B estimates the estimated voltage of the battery 13 and the circumferential temperature of the battery 13 detected by the second detecting means 19 when the measuring means B measures the terminal voltage of the battery 13, wherein the revised value of the residual voltage drop revised by the revising means 23F is added to the value of the estimated voltage of the battery 13 estimated by the estimating means 23B, thereby a present charging capacity of the battery 13 is computed.
According to the apparatus for computing a battery capacity of the first aspect of the present invention, when the temperature around the battery 13 changes, the battery capacity also changes to change the terminal voltage of the battery 13, therefore if the temperature around the battery 13 is different between at a time when the open circuit voltage of the battery 13 memorized in the second memory means 25 is calculated and at a time when the estimated voltage of the battery 13 is estimated by the estimating means 23B after the first detecting means A detects that the discharge current of the battery 13 judged to be in the equilibrium state by the judging means 23C starts decreasing from the predetermined large current value, the terminal voltage component reflected in the open circuit voltage in response to the temperature around the battery 13 is different from the terminal voltage component reflected in the estimated voltage in response to the temperature around the battery 13.
However, even if the temperature around the battery 13 detected by the second detecting means 19 at a time when the open circuit voltage memorized in the second memory means 25 is calculated is different from the temperature around the battery 13 detected by the second detecting means 19 at a time when the estimated voltage of the battery 13 is estimated by the estimating means 23B after the first detecting means A detects that the discharge current of the battery 13 judged to be in the equilibrium state by the judging means 23C starts decreasing from the predetermined large current value, the value of the residual voltage drop memorized by the first memory means 27 is revised in response to both temperatures around the battery 13 described above by the revising means 23F so as to compute the present charging capacity of the battery 13 by using the revised value of the residual voltage drop, thereby the present charging capacity of the battery 13 is computed in a state that the changeable component of the terminal voltage changeable due to the difference in the temperature around the battery is removed, by using the open circuit voltage and estimated voltage, in which the terminal voltage component in response to the temperature around the battery is reflected in the same condition.
Preferably, regarding the apparatus according to the first aspect of the present invention, the predetermined large current value is a current value required upon a start of a starter motor of the vehicle,
the apparatus further comprises third detecting means C for detecting that the discharge current of the battery 13, which is detected by the first detecting means A as to start decreasing from the predetermined large current value, decreases to a target current value not less than a maximum discharge current value when loads of the vehicle except a starter motor are driven,
wherein after the first detecting means A detects that the discharge current of the battery 13 starts to decrease from the predetermined large current value, the first calculating means 23A calculates the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery 13 until the third detecting means C detects that the discharge current of the battery 13 decreases to the target current value.
According to the apparatus for computing a battery capacity of the first aspect of the present invention, even if the electric power from the battery 13 is simultaneously supplied to a plurality of the other loads of the vehicle, the current value required upon the start of the starter motor 5 exceeds the current value thereof, therefore if the current value required upon the start of the starter motor 5 is set up to be the predetermined large current value, at a time when the first detecting means A detects that the discharge current of the battery 13 during the constant load discharge starts decreasing from the predetermined large current value, before that time the discharge current once reaches the predetermined large current and the terminal voltage of the battery 13 is subjected to the voltage drop exceeding the voltage drop due to the polarization of the discharge side arisen due to the former discharge.
At a time when the third detecting means C detects that the discharge current decreases from the predetermined large current value to the target current value not less than the maximum discharge current value upon the driving of the loads except the starter motor 5, the voltage drop due to the polarization of the discharge side remaining in the terminal voltage of the battery 13 in that state does not seemingly contain the voltage drop component due to the polarization of the discharge side arisen due to the power supply to the loads of the vehicle except the starter motor 5, therefore only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, seemingly appears.
Consequently, the first calculating means 23A calculates the voltage-current characteristic of the battery 13 from the terminal voltage and discharge current, which are periodically measured after the first detecting means A detects that the discharge current of the battery 13 starts decreasing from the predetermined large current value until the third detecting means C detects that the discharge current of the battery 13 decreases to the target current value. The estimated voltage estimated by the estimating means 23B from the voltage-current characteristic purely reflects only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, even if the loads of the vehicle except the starter motor 5 is still driven.
The second aspect of the present invention is also an apparatus for computing a battery capacity executing the steps of:
periodically measuring a terminal voltage and a discharge current of a battery 13 that supplies an electric power to loads in a vehicle when the battery 13 is subjected to a constant load discharge by using a predetermined large current value corresponding to a maximum supplying electric power value to the loads;
calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
estimating an estimated voltage that is an estimated terminal voltage of the battery 13 in a constant load discharging state thereof from the voltage-current characteristic; and
computing a charging capacity of the battery 13 from the estimated voltage,
wherein the apparatus comprises:
first detecting means A for detecting a start of a decrease in the discharge current from the predetermined large current value in the constant load discharge process of the battery 13 by using the predetermined large current value;
first calculating means 23A for calculating the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery 13 after the first detecting means A detects the start of the decrease in the discharge current; and
estimating means 23B for estimating the estimated voltage of the battery 13 in the constant load discharge process of the battery 13 by using the predetermined large current value, on the basis of the voltage-current characteristic calculated by the first calculating means 23A, thereby the charging capacity of the battery 13 is computed by using the estimated voltage of the battery 13 estimated by the estimating means 23B.
According to the apparatus for computing a battery capacity of the second aspect of the present invention, once the discharge current of the constant load discharge reaches the predetermined large current value corresponding to the maximum supply electric power value to the loads of the vehicle, even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, the system is in a state that the polarization of the discharge side corresponding to the predetermined large current value, which exceeds the residual voltage drop, arises or in a state that the polarization of the discharge side, the magnitude of which corresponds to the predetermined large current value, newly arises after the residual voltage rise is canceled off.
On the other hand, even if the battery 13 in an equilibrium state is subjected to the constant load discharge with the predetermined large current value, when the discharge current reaches the predetermined large current value, the polarization arises, the magnitude of which corresponds to the predetermined large current value.
Therefore, when the battery 13 is subjected to the constant load discharge with the predetermined large current value, not depending upon that the battery 13 was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled off, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery 13 while the discharge current is decreasing from the predetermined large current value, is the same.
When the battery 13 implements the constant load discharge with the predetermined large current value, each time the first detecting means A detects a start of a decrease in the discharge current of the battery 13 from the predetermined large current value, the first calculating means 23A calculates the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery 13, which are periodically measured while the discharge current decreases from the predetermined large current value and measured under the condition that the influence of the residual voltage drop or rise is removed even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, then the estimating means 23B estimates the estimated voltage of the battery 13 in the constant load discharge process of the battery with the predetermined large current value, on the basis of the voltage-current characteristic calculated by the first calculating means 23A with removing the influence of the polarization arisen in the former discharge, thereby the present state of charge of the battery 13 is computed from the value of the estimated voltage estimated by the estimating means 23B.
Preferably, regarding the apparatus according to the second aspect of the present invention, the predetermined large current value is a current value required upon a start of a starter motor of the vehicle.
According to the apparatus for computing a battery capacity of the second aspect of the present invention, even if the electric power from the battery 13 is simultaneously supplied to a plurality of the other loads of the vehicle, the current value required upon the start of the starter motor exceeds the current value thereof, therefore if the current value required upon the start of the starter motor is set up to be the predetermined large current value, at a time when the first detecting means A detects that the discharge current of the battery 13 upon the constant load discharge starts decreasing from the predetermined large current value, before that time the discharge current once reaches the predetermined large current and the battery 13 is in a state that the polarization of the discharge side, which is large enough for canceling the polarization arisen due to the former charge and discharge, arises.
Preferably, regarding the apparatus according to the second aspect of the present invention, the apparatus further comprises
third detecting means C for detecting that the discharge current of the battery 13, for which the first detecting means A detects that the discharge current starts decreasing from the predetermined large current value, decreases to a target current value not less than a maximum discharge current value when loads of the vehicle except a starter motor are driven,
wherein after the first detecting means A detects that the discharge current of the battery 13 starts to decrease from the predetermined large current value, the first calculating means 23A calculates the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery 13 until the third detecting means C detects that the discharge current of the battery 13 decreases to the target current value.
According to the apparatus for computing a battery capacity of the second aspect of the present invention, at a time when the third detecting means C detects that the discharge current decreases from the predetermined large current value to the target current value not less than the maximum discharge current value upon the driving of the loads except the starter motor 5, the voltage drop due to the polarization of the discharge side remaining in the terminal voltage of the battery 13 in that state does not seemingly contain the voltage drop component due to the polarization of the discharge side arisen due to the power supply to the loads of the vehicle except the starter motor 5, therefore only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, seemingly appears.
Consequently, the first calculating means 23A calculates the voltage-current characteristic of the battery 13 from the terminal voltage and discharge current, which are periodically measured after the first detecting means A detects that the discharge current of the battery 13 starts decreasing from the predetermined large current value until the third detecting means C detects that the discharge current of the battery 13 decreases to the target current value. The estimated voltage estimated by the estimating means 23B from the voltage-current characteristic purely reflects only the remaining component after excluding the component of the voltage drop due to the polarization of the discharge side caused by the discharge with the predetermined large current value, which is canceled out due to the decrease in the discharge current to the target current value, even if the loads of the vehicle except the starter motor 5 is still driven.